Friction stir welding method, and hollow shape member for friction stir welding

ABSTRACT

Face plates  11  and  12  of a hollow shape member  10  are abutted against face plates  21  and  22  of a hollow shape member  20 . Grooves  18  formed to said face plates  11  and  12  at the abutted region receive projections  28  formed to said face plates  21  and  22 . A connecting plate  14  orthogonal to said face plates  11  and  12  is provided to the hollow shape member  10 . There is no connecting plate orthogonal to face plates  21  and  22  disposed on the end of the hollow shape member  20 . Friction stir welding heat causes the face plate  21  ( 22 ) to move toward the thickness direction of hollow shape members  10  and  20 , but such movement is suppressed by the groove  18  and projection  28 . Thereby, the abutted region is welded flatly. Since the hollow shape member  20  requires no connecting plate corresponding to plate  14 , the welded members are light in weight.

FIELD OF THE INVENTION

[0001] The present invention relates to a friction stir welding methodthat is especially preferable for welding hollow shape members, and tohollow shape members suitable for such friction stir welding method.

DESCRIPTION OF THE RELATED ART

[0002] Friction stir welding is a method performed by rotating andinserting a round shaft (called a rotary tool) to a joint region betweenmembers to be welded, and moving the same along the joint line, therebyheating, softening, plasticizing, and solid-phase welding the jointregion. The rotary tool comprises a large-diameter portion and asmall-diameter portion. The small-diameter portion is inserted to themember(s) to be welded, and the end surface of the large-diameterportion is disposed so as to contact the member(s). The small-diameterportion is provided with a screw thread.

[0003] Projections protruding to the side from which the rotary tool isinserted are formed to the two members to be welded, and the metalmaterial constituting the projections is used as the source material tofill the gap between the two members. The large-diameter portion of therotary tool is inserted to the projections.

[0004] Since the rotary tool is inserted to the metal material at theabutted region, a great force is added to the joint region. Therefore,upon welding hollow shape members, the area of one hollow shape memberwhere a connecting plate that connects the two face plates exists isselected to be welded with the other hollow shape member. This isbecause the connecting plates can provide support against theabove-mentioned force, thereby preventing deformation of the hollowshape members during the friction stir welding.

[0005] The above mentioned prior art method is disclosed in JapanesePatent Laid-Open Publication Nos. 9-309164 (309164/97, EP 0797043A2),and 11-90655 (90655/99, U.S. Pat. No. 6050474).

[0006] When welding (or friction stir welding) the joint region betweentwo abutted plates, the plates are deformed by the weld heat. Oneexample of such deformation is the deformation in the thicknessdirection of the plates. Such deformation may cause unevenness betweenone plate and the other plate being welded, deteriorating the flatnessof the plate surface. Therefore, in welding hollow shape members, themembers being welded is equipped with a connecting plate that connectsthe two parallel face plates positioned near the joint region to bewelded, thus preventing the face plates from deforming in the thicknessdirection. Such connecting plate is positioned near the weld region ofeach hollow member. The connecting plate is orthogonal to the faceplates.

[0007] The welding temperature of the friction stir weld is low comparedto arc welding, so there is less fear of deformation, but deformationstill occurs. Therefore,connecting plates are provided to the weldregion according to the above-mentioned JP Laid-Open Publications No.309164/97 (EP 0797043A2) and No. 90655/99 (U.S. Pat. No. 6050474).According to the disclosure of 90655/99(U.S. Pat. No. 6050474), each ofthe hollow shape members being welded are provided with a connectingplate positioned at the end region thereof. Though the connecting platesare required to provide necessary strength to the hollow shape members,the connecting plates also inevitably increase the mass of the members.

[0008] In 309164/97(EP 0797043A2), only one of the two hollow shapemembers being friction stir welded is provided with the connectingplate.

[0009] The object of the present invention is to provide a friction stirwelding method that realizes a good weld with a light-weight member, anda hollow shape member used for such method.

SUMMARY OF THE INVENTION

[0010] The first method for achieving the objects of the presentinvention characterizes in that an end portion in the width direction ofa first hollow shape member is abutted against an end portion in thewidth direction of a second hollow shapemember; the first hollow shapemember comprises two face plates; a first connecting plate forconnecting the two plates, at least one end of which is connected to aregion other than the end portion; a second connecting plate forconnecting the end portions of the face plates that is disposedsubstantially orthogonal to the face plates; recessed portions formedrespectively to connecting portions where the two face plates are eachconnected with the second connecting plate, each recessed portionopening outward toward both the width direction and the thicknessdirection of the hollow shape member; a groove or projection formed toone recessed portion; and a groove or projection formed to the otherrecessed portion; the second hollow shape member comprises two faceplates; a first connecting plate for connecting the two plates, at leastone end of which is connected to a region other than the end portion; aprojection or groove formed to one face plate at the end portion of thehollow member; and a projection or groove formed to the other face plateat the end portion of the hollow member; the projections are eachinserted to a corresponding groove, respectively, when the two hollowmembers are abutted against each other, at which time one hollow shapemember is inserted to the other hollow shape member so as tosubstantially suppress movement of the hollow shape member in thethickness direction; and a rotary tool is disposed on the extension ofplate thickness of the second connecting plate, thereby friction stirwelding the abutted region from the outer direction of thickness of thehollow shape members.

[0011] The second method for achieving the objects of the presentinvention characterizes in that an end portion in the width direction ofa first hollow shape member is abutted against an end portion in thewidth direction of a second hollow shape member; the first hollow shapemember comprises two face plates; a first connecting plate forconnecting the two plates, at least one end of which is connected to aregion other than the end portion; a second connecting plate forconnecting the end portions of the face plates that is disposedsubstantially orthogonal to the face plates; recessed portions formedrespectively to connecting portions where the two face plates are eachconnected with the second connecting plate, each recessed portionopening outward toward both the width direction and the thicknessdirection of the hollow shape member; a groove or projection formed toone recessed portion; and a groove or projection formed to the otherrecessed portion; the second hollow shape member comprises two faceplates; a first connecting plate for connecting the two plates, at leastone end of which is connected to a region other than the end portion;one face plate having at the end portion of the hollow shape membereither a projection protruding outward to the width direction of thehollow shape member or a groove opening outward to that direction ; andthe other face plate having at the end portion of the hollow shapemember either a projection protruding outward to the width direction ofthe hollow shape member or a groove opening outward to that direction;the projections are each inserted to a corresponding groove,respectively, when the two hollow members are abutted against eachother; and a rotary tool is disposed on the extension of plate thicknessof the second connecting plate, thereby friction stir welding theabutted region from the outer direction of thickness of the hollow shapemembers.

[0012] The third method achieving the objects of the present inventioncharacterizes in that an end portion in the width direction of a firsthollow shape member is abutted against an end portion in the widthdirection of a second hollow shape member; the first hollow shape membercomprises two face plates, the two plates each having either a grooveopening toward the width direction or a projection protruding toward thewidth direction, formed at one width-direction-end of the first hollowshape member; the second hollow shape member comprises two face plates,the two face plates each having either a projection protruding towardthe width direction or a groove opening toward the width direction,formed at one width-direction-end of the second hollow shape member; theprojections are each inserted to a corresponding groove, respectively,when the two hollow members are abutted against each other; and thefriction stir welding is performed to weld said abutted regions, and thegrooves and the projections.

[0013] Moreover, one hollow shape member for achieving the objects ofthe present invention comprises two face plates; a first connectingplate for connecting the two face plates, at least one end of which isconnected to a region other than an end portion in the width directionof the hollow shape member; a second connecting plate for connecting theend portions of the two face plates, disposed substantially orthogonalto the face plates; recessed portions provided respectively to each ofthe two connecting portions where the two face plates are connected withthe second connecting plate, each recessed portion opening outwardtoward both the width direction and the thickness direction of thehollow shape member; and either grooves opening toward the outerdirection of width or projections protruding toward the outer directionof width formed to the recessed portions, respectively.

[0014] The other hollow shape member for achieving the object of thepresent invention comprises two face plates; a connecting plate forconnecting the two face plates, at least one end of which is connectedto a position other than an end portion in the width direction of thehollow shape member; either a projection protruding toward or a grooveopening toward the outer direction of width of the hollow shape member,provided to the end of a first face plate at the end portion in thewidth direction of the hollow shape member; and either a projectionprotruding toward or a groove opening toward the outer direction ofwidth of the hollow shape member, provided to the end of a second faceplate at the end portion in the width direction of the hollow shapemember.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a vertical cross-sectional view of the joint region ofthe hollow shape members according to one embodiment of the presentinvention;

[0016]FIG. 2 is a vertical cross-sectional view showing the whole jointregion of the hollow shape members of FIG. 1;

[0017]FIG. 3 is a perspective view showing the car body of the railwaycar;

[0018]FIG. 4 is a vertical cross-sectional view showing the joint regionof the hollow shape member 10 according to another embodiment of theinvention; and

[0019]FIG. 5 is a vertical cross-sectional view showing the joint regionof the hollow shape member 20 used in the joint region of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] The first embodiment of the present invention will be explainedwith reference to FIGS. 1 to 3. A car body 500 of a railway carcomprises side structures 501 that constitute the sides thereof, a roofstructure 502 that constitutes the roof thereof, an underframe 503 thatconstitutes the floor thereof, and end structures 504 that define thelongitudinal ends thereof. The side structures 501, the roof structure502, and the under frame 504 are each formed by welding plural extrudedmembers 10, 20. A plural number of extruded members are arranged alongthe periphery of the car body 500, with the longitudinal direction(extruded direction) of the extruded members 10 and 20 oriented alongthe longitudinal direction of the car body 500. The extruded members 10and 20 are hollow shape members made of aluminum alloy.

[0021] The joint region between the hollow shape members 10 and 20constituting the side structure 501 will now be explained. The jointsbetween the hollow shape members of other portions are formed in asimilar manner.

[0022] The hollow shape member 10 (20) comprises two substantiallyparallel face plates 11 (21) and 12 (22), and plural connecting plates13 (23) and 14 that connect the two face plates. The connecting plates13 (23) are sloped against the face plates 11 (21) and 12 (22). In otherwords, the face plates 11 (21) and 12 (22) and the connecting plates 13(23) are arranged in trusses. According to where the hollow shape member10 or 20 is to be placed, one of the face plates 11 (21) can be slopedor curved in an arc-shape against the other face plate 12 (22), or eventhe whole hollow shape member can be curved in an arc-shape.

[0023] The connecting plate 14 positioned at the width-direction-end ofthe hollow shape member 10 is substantially orthogonal to the faceplates 11 and 12. However, the hollow shape member 20 does not have aconnecting plate orthogonal to the face plates 21 and 22 at the endportion thereof. The connecting portions where the connecting plate 14come into contact with the face plates 11 and 12 are provided withrecessed portions that receive the end portion of the face plates 21 and22 of the hollow shape member 20. Each connecting portion is providedwith a protruded block 15 that supports the face plate 21 or 22. Theprotruded block 15 is protruded from the connecting plate 14 toward thewidth-direction-end of the hollow shape member 10. The recessed portionis defined by the face plate 11 (12), the connecting plate 14, and theprotruded block 15. The recessed portion is opened outward toward thewidth direction and the thickness direction of the hollow shape member10. When face plates 21 and 22 are placed (superposed) on the recessedportions, the end surface of the face plates 21, 22 and the end surfaceof the face plates 11, 12 are abutted against each other.

[0024] The face plates 11 and 12 (21 and 22) are each provided with aprojection 17 (27) that protrudes outward to the direction of thicknessof the hollow shape members 10 and 20 at the end portion thereof,respectively. The end surface of the face plates 11 and 12 (21 and 22)and the end surface of the projection 17 (27) are arranged along thethickness direction of the hollow shape member 10 (20). The end surfacesof the face plates 11, 12 and the projections 17 formed thereto (thewidth-direction-end of the hollow shape member 10) are disposed on theextension of the center line of thickness C of the connecting plate 14.The end surface of the face plates 21, 22 and the projections 27 formedthereto are also disposed on the extension of the thickness center C ofthe connecting plate 14.

[0025] When the hollow shape members 10 and 20 are assembled, the endsurfaces of the face plates 11, 12, 21 and 22 and projections 17, 17, 27and 27 are all disposed on the extension of the thickness center C ofthe connecting plate 14. According to this assembly, the end surface ofthe face plate 11 (12) and the projection 17 (17) of the hollow member10 is abutted against the end surface of the face plate 21 (22) and theprojection 27 (27) of the hollow shape member 20. The hollow shapemembers are designed so that when member 10 and 20 are abutted againsteach other, the gap formed at the abutted portion is minimum. In otherwords, the space formed between the face plates 21, 22 and the recessedportions is determined in advance.

[0026] When the hollow shape members 10 and 20 are abutted against eachother, the outer surface of the face plates 11 and 12 are flush with theouter surface of the face plates 21 and 22, and the protruding height ofthe projections 17 and 27 are equal. The width of the two projections 17and 27 are also equal. The total width of the two projections 17 and 27is greater than the diameter of the large-diameter portion 51 of therotary tool 50. The metal material of the projections 17 and 27 serve asthe source material for filling the gap formed at the abutted portion.

[0027] The abutted end surface of the hollow member 10 (the surface ofthe recessed portion disposed along the thickness direction of thehollow member 10 (the surface substantially orthogonal to the faceplates 11 and 12, disposed along center line C)) is provided withgrooves 18, 18 disposed along the longitudinal direction of the hollowshape member 10. The abutted end surface of the hollow shape member 20(the surface substantially orthogonal to the face plates 21 and 22,disposed along center line C) is provided with projections 28, 28disposed along the longitudinal direction of the hollow shape member 20.The projections 28, 28 fit into the grooves 18, 18.

[0028] In order for the projections 28 to be easily inserted to thegrooves 18, the grooves 18 and the projections 28 are formed intrapezoidal shapes. The projection 28 is designed so that the endportion thereof is smaller in width than the base portion. The groove 18is designed so that the bottom portion thereof is smaller in width thanthe opening portion. All the corners of the groove 18 and the projection28 are rounded. The sizes of the projections 28 and the grooves 18 aredetermined so that when the hollow shape members are assembled, the gapformed between the projection and the groove is very small. Especiallythe gap formed between the groove 18 and the projection 28 in thethickness direction of the hollow shape members 10 and 20 should be verysmall. It is preferable that the groove 18 and the projection 28 are incontact with each other in the thickness direction of the hollow shapemembers 10 and 20.

[0029] The position of the groove 18 (projection 28) in the thicknessdirection of the hollow member 10 (20) should be set within the totalrange of thickness of the face plate 11 or 12 (21 or 22) and theprojections 17, 17 (27, 27).

[0030] The plate thickness of the face plates 11, 12, 21 and 22 at theabutted portions is thicker than the other areas. Since the outersurface in the thickness direction of the hollow shape members shouldsubstantially be flat, the plate thickness is increased by forming aprotruded area projecting to the inner side of the face plates. Thethickness of the protrusion is reduced gradually as it recedes from theabutted portion. The bottom surface of the recessed portion issubstantially parallel to the outer surfaces of the surface plates 11,12 and 21, 22.

[0031] Upon welding the hollow shape members 10 and 20, the two membersare assembled to fit to each other as shown in FIG. 1. The projections28, 28 are inserted to the grooves 18, 18. Since the grooves 18 areopened toward the width-direction-end of the hollow member and theprojections 28 are protruded toward the width-direction-end of thehollow member, they fit into one another easily.

[0032] After assembly, the hollow shape members 10 and 20 are fixedimmovably on a bed 100. Reference number 101 shows a groove into whichthe projections 17 and 27 positioned on the lower surface of the members10 and 20 enter. After fixing the members, the upper surface of theabutted region is temporarily welded intermittently.

[0033] The rotary tool 50 is equipped with a small-diameter portion 52formed on the end of a large-diameter portion 51. The small-diameterportion 52 is provided with as crew thread. Upon welding the members,the rotary tool 50 is inserted to the abutted region. The central axisof the rotary tool 50 is positioned on the extension of the platethickness center C of the connecting plate 14. The lower end of thelarge-diameter portion 51 is disposed between the extension of the outersurface of the face plates 11 and 21 (12 and 22) and the upper surfaceof the projections 17 and 27 (17 and 27). The small-diameter portion 52is inserted to the abutted region between the face plate 11 (12) and theface plate 21 (22). The lower end of the small-diameter portion 52 isinserted somewhat deeper than the upper surface of the protruding block15 (bottom surface of the recess). At a minimum, the small-diameterportion 52 should be inserted to a depth enabling the protruded block 15to be plasticized.

[0034] When the central axis of the rotary tool 50 is disposed on theextension of the plate thickness center C of the connecting plate 14,the groove 18 is positioned within the diameter range of thesmall-diameter portion 52. The projection 28 is also positioned withinthe diameter range of the small-diameter portion 52. While maintainingthis condition, the rotary tool 50 is rotated and moved along the jointline of the abutted region.

[0035] When friction stir welding of one side surface is finished, thehollow shape members 10 and 20 are turned upside down, and friction stirwelding is similarly performed to the other side.

[0036] Next, the projections 17 and 27 positioned on the outer surfaceof the car body 500 is cut off so that the outer surface of the joint isflush with the outer wall of the face plates 11 and 21 (12 and 22).

[0037] According to the present invention, even if the face plate 21(22) is softened by the friction heat generated by the friction stirwelding that may lead to deformation, the movement of the face plate 21(22) in the vertical direction is either prevented or suppressed by thepresent structure where the projections 28 fit into the grooves 18.Therefore, a weld having minimum unevenness is realized at the jointbetween the face plates 11 (12) and 21 (22).

[0038] According to the above-mentioned method, less work is required tocut off any uneven bumps formed after the friction stir welding to thejoint region. Therefore, the present invention can be performed at a lowcost. Moreover, it is possible to omit in advance a connecting platedisposed on the end region of the hollow shape member 20 orthogonal tothe face plates 21 and 22. Thus, a light-weight hollow member 20 can bemanufactured at a low cost.

[0039] When placing the central axis of the rotary tool 50 on theextension of the plate thickness center C of the connecting plate 14,the groove 18 is disposed within the diameter range of thesmall-diameter portion 52. The projection 28 is also disposed within thediameter range of the small-diameter portion 52. Therefore, even whenthere is a gap formed between the groove 18 and the projection 28, thegap can be filled when welding the joint region. The position and sizeof the groove 18 and the projection 28 are determined so that even ifthe groove 18 and the projection 28 are not disposed within the diameterrange of the small-diameter portion 52, the groove 18 and the projection28 are plasticized by the rotation of the small-diameter portion.

[0040] Since the rotary tool 50 is placed on the extension of the platethickness of the connecting plate 14, the load provided to the membersat the time of friction stir welding is supported by the connectingplate 14, and the deformation of the joint region is minimized. Theconnecting plate 14 is formed to provide enough rigidity to support suchload. It is best that the central axis of the rotary tool 50 bepositioned on the extension of the plate thickness center C of theconnecting plate 14.

[0041] Since a portion of the groove 18 and projection 28 is formed inthe projections 17 and 27 disposed outside of the extension of the outersurface of the face plates 11, 21, 12 and 22 excluding the projectedportions of projections 17 and 27 (the portion of the projections 17 and27 that stick out beyond the outer surface), it is easy to form a groove18 and a projection 28 having a determined size.

[0042] It is preferred that the central axis of the rotary tool 50 andthe ends of the projections 17 and 27 are substantially disposed alongthe extension of the center line C of plate thickness of the connectingplate 14.

[0043] According to the above-mentioned embodiment, the groove 18 isformed to the recessed portion on the hollow shape member 10, and theprojection 28 is formed on the hollow shape member 20, but it is alsopossible to provide a projection 28 to the recessed portion of thehollow shape member 10 and to provide a groove 18 to the ends of faceplates 21 and 22 of the hollow shape member 20. However, it isconsidered that the former design is easier to realize a precise shapewhen creating the members by extrusion.

[0044] Moreover, it is possible to provide a groove 18 to the side ofone face plate 11 (one recessed portion) and provide a projection 28 tothe side of the other face plate 12 (the other recessed portion), and toprovide a projection 28 to one face plate 21 and provide a groove 18 tothe other face plate 22.

[0045] The embodiment shown in FIGS. 4 and 5 will now be explained. Thecenter of depth of the groove 18 is disposed on the extension of theplate thickness center C of the connecting plate 14. Therefore, the endsurface of the face plates 11, 12 and the projection 17 at the abuttingregion is protruded toward the end of the hollow shape member 10 fromthe plate thickness center C of the connecting plate 14. The abuttingregion of the hollow member 20 is formed correspondingly. In otherwords, the end surface of the face plates 21 and 22 and the projection27 at the abutting region (excluding the projection 28) protrudes towardthe other end side of the width direction of the hollow shape member 10from the plate thickness center C of the connecting plate 14. Therefore,the width of the projection 17 is wider than that of the projection 27.

[0046] Friction stir welding is performed while the central axis of therotary tool 50 is disposed on the extension of the plate thicknesscenter C of the connecting plate 14. Upon friction stir welding, theposition of the abutted region between projections 17 and 27 isdetected, and the position of the rotary tool 50 is determined basedthereon, the position being biased for a predetermined distance towardthe hollow shape member 10 from the abutted region.

[0047] Accordingly, the allowance of the deviation range of the centralaxis position of the rotary tool 50 (small-diameter portion 52) againstthe groove 18 and projection 28 is increased.

[0048] It is preferred that the central axis of the rotary tool 50 andthe center of depth of the groove 18 are substantially disposed on theextension of the plate thickness center C of the connecting plate 14.

[0049] Each preferred embodiment of the present invention requires aconnecting plate 14 to support the load added to the welded members whenfriction stir welding is performed. However, if a support member capableof supporting such load is arranged in the space defined by the faceplates 11, 12, 21, and 22 and the connecting plates 13 and 23, theconnecting plate 14 becomes unnecessary, and can be omitted. Theposition of the width-direction-ends of the hollow shape members 10 and20 (the position of the grooves 18 and projections 28, in other words,the position of the abutted region) are substantially the same. Thesupport member is mounted for example on the lower face plates 12, 22.

[0050] The technical scope of the present invention is not restricted bythe terms used in the claims or in the summary of the present invention,and is extended to the range in which a person in the art could easilysubstitute based on the present disclosure.

[0051] The present invention enables to realize a light-weight frictionstir weld having good quality.

What is claimed is:
 1. A friction stir welding method, characterized inthat: an end portion in the width direction of a first hollow shapemember is abutted against an end portion in the width direction of asecond hollow shape member; the first hollow shape member comprises twoface plates; a first connecting plate for connecting the two plates, atleast one end of which is connected to a region other than said endportion; a second connecting plate for connecting said end portions ofsaid face plates that is disposed substantially orthogonal to said faceplates; recessed portions formed respectively to connecting portionswhere said two face plates are each connected with said secondconnecting plate, each recessed portion opening outward toward both thewidth direction and the thickness direction of the hollow shape member;a groove or projection formed to one recessed portion; and a groove orprojection formed to the other recessed portion; the second hollow shapemember comprises two face plates; a first connecting plate forconnecting the two plates, at least one end of which is connected to aregion other than said end portion; a projection or groove formed to oneface plate at said end portion of said hollow member; and a projectionor groove formed to the other face plate at said end portion of saidhollow member; said projections are each inserted to a correspondinggroove, respectively, when said two hollow members are abutted againsteach other, at which time one hollow shape member is inserted to theother hollow shape member so as to substantially suppress movement ofsaid hollow shape member in the thickness direction; and a rotary toolis disposed on the extension of plate thickness of said secondconnecting plate, thereby friction stir welding said abutted region fromthe outer direction of thickness of said hollow shape members.
 2. Afriction stir welding method according to claim 1, wherein said frictionstir welding is performed to weld said abutted region, and said groovesand said projections, respectively.
 3. A friction stir welding method,characterized in that: an end portion in the width direction of a firsthollow shape member is abutted against an end portion in the widthdirection of a second hollow shape member; the first hollow shape membercomprises two face plates; a first connecting plate for connecting thetwo plates, at least one end of which is connected to a region otherthan said end portion; a second connecting plate for connecting said endportions of said face plates that is disposed substantially orthogonalto said face plates; recessed portions formed respectively to connectingportions where said two face plates are each connected with said secondconnecting plate, each recessed portion opening outward toward both thewidth direction and ard the thickness direction of the hollow shapemember; a groove or projection formed to one recessed portion; and agroove or projection formed to the other recessed portion; the secondhollow shape member comprises two face plates; a first connecting platefor connecting the two plates, at least one end of which is connected toa region other than said end portion; one face plate having at the endportion of said hollow shape member either a projection protrudingoutward to the width direction of said hollow shape member or a grooveopening outward to said direction; and the other face plate having atthe end portion of said hollow shape member either a projectionprotruding outward to the width direction of said hollow shape member ora groove opening outward to said direction; said projections are eachinserted to a corresponding groove, respectively, when said two hollowshape members are abutted against each other; and a rotary tool isdisposed on the extension of plate thickness of said second connectingplate, thereby friction stir welding said abutted region from the outerdirection of thickness of said hollow shape members.
 4. A friction stirwelding method according to claim 3, wherein said friction stir weldingis performed to weld said abutted regions, and said grooves and saidprojections, respectively.
 5. A friction stir welding method accordingto claim 4, wherein said groove and said projection is disposed withinthe range of diameter of a small-diameter portion of said rotary toolbeing inserted to said hollow shape members upon performing the frictionstir welding.
 6. A friction stir welding method according to claim 5,wherein the central axis of said rotary tool is disposed within therange of depth of said groove upon performing the friction stir welding.7. A friction stir welding method according to claim 4, wherein thecentral axis of said rotary tool is disposed within the range of depthof said groove upon performing the friction stir welding.
 8. A frictionstir welding method according to claim 3, wherein grooves are formed tothe recessed portions of said first hollow shape member as said groovesor projections; and projections are formed to the two face plates ofsaid second hollow shape member as said grooves or projections.
 9. Afriction stir welding method, characterized in that: an end portion inthe width direction of a first hollow shape member is abutted against anend portion in the width direction of a second hollow shape member; saidfirst hollow shape member comprises two face plates, said two faceplates each having either a groove opening toward the width direction ora projection protruding toward the width direction, formed at onewidth-direction-end of said first hollow shape member; said secondhollow shape member comprises two face plates, said two face plates eachhaving either a projection protruding toward the width direction or agroove opening toward the width direction, formed at onewidth-direction-end of said second hollow shape member; said projectionsare each inserted to a corresponding groove, respectively, when said twohollow members are abutted against each other; and said friction stirwelding is performed to weld said abutted regions, and said grooves andsaid projections.
 10. A friction stir welding method according to claim9, wherein said groove and said projection is disposed within the rangeof diameter of a small-diameter portion of said rotary tool beinginserted to said hollow shape member upon performing the friction stirwelding.
 11. A friction stir welding method according to claim 10,wherein the central axis of said rotary tool is disposed within therange of depth of said groove upon performing the friction stir welding.12. A friction stir welding method according to claim 9, wherein thecentral axis of said rotary tool is disposed within the range of depthof said groove upon performing the friction stir welding.
 13. A hollowshape member for friction stir welding, comprising: two face plates; afirst connecting plate for connecting said two face plates, at least oneend of which is connected to a region other than an end portion in thewidth direction of the hollow shape member; a second connecting platefor connecting said end portions of said two face plates, disposedsubstantially orthogonal to said face plates; recessed portions providedrespectively to each of the two connecting portions where said two faceplates are connected with said second connecting plate, each recessedportion opening outward toward both the width direction and thethickness direction of said hollow shape member; and either groovesopening toward the outer direction of width or projections protrudingtoward the outer direction of width formed to said recessed portions,respectively.
 14. A hollow shape member for friction stir weldingaccording to claim 13, wherein said grooves or said projections aredisposed on the extension of plate thickness of said first connectingplate.
 15. A hollow shape member for friction stir welding according toclaim 13, wherein said grooves or said projections are disposed on theextension of substantially the center of plate thickness of said secondconnecting plate.
 16. A hollow shape member for friction stir weldingaccording to claim 13, wherein either the center of depth of saidgrooves or the center of protruded height of said projections isdisposed on the extension of substantially the center of plate thicknessof said second connecting plate.
 17. A hollow shape member for frictionstir welding according to claim 13, wherein: second projections areprovided to the end portion with said recessed portion of a first faceplate and to the end portion with said recessed portion of a second faceplate, respectively, each second projection protruding outward to thethickness direction; and a portion of said grooves or a portion of saidprojections is disposed within the range of protruded height of eachsecond projection, respectively.
 18. A hollow shape member for frictionstir welding according to claim 13, wherein said recessed portions areprovided with said grooves, respectively, as said grooves orprojections.
 19. A hollow shape member for friction stir weldingaccording to claim 13, wherein said recessed portions are provided withsaid projections, respectively, as said grooves or projections.
 20. Ahollow shape member for friction stir welding, comprising: two faceplates; a connecting plate for connecting said two face plates, at leastone end of which is connected to a position other than an end portion inthe width direction of the hollow shape member; either a projectionprotruding toward or a groove opening toward the outer direction ofwidth of said hollow shape member, provided to the end of a first faceplate at said end portion in the width direction of said hollow shapemember; and either a projection protruding toward or a groove openingtoward the outer direction of width of said hollow shape member,provided to the end of a second face plate at said end portion in thewidth direction of said hollow shape member.
 21. A hollow shape memberfor friction stir welding according to claim 20, wherein the endportions of said first and second face plates are provided withprojections, respectively, as said projections or grooves.
 22. A hollowshape member for friction stir welding according to claim 20, whereinthe end portions of said first and second face plates are provided withgrooves, respectively, as said projections or grooves.
 23. A hollowshape member for friction stir welding according to claim 20, wherein:second projections are provided to the end portions of the first andsecond face plates having said projections or said grooves,respectively, both second projections protruding outward to thethickness direction; and a portion of said projections or said groovesis disposed within the range of protruded height of said secondprojections, respectively.
 24. A hollow shape member for friction stirwelding according to claim 20, wherein the end portions of said firstand second face plates having said projections or said grooves,respectively, are substantially disposed at the same position in thewidth direction of said hollow shape member.